Building a better oil trap

Every year, millions of gallons of used motor oil are leaked, spilled and illegally dumped onto roads, parking lots and driveways throughout California. When it rains, storm run-off carries the oil into curbside drains that flow directly into nearby waterways, with toxic effects on the environment.

Civil engineering professor John Johnston, staff research engineer Brian Currier from the University’s Office of Water Programs, and a handful of student assistants are studying methods for removing oil from stormwater run-off before it reaches neighboring ecosystems.

The team began with a yearlong study of how well drain inlet inserts—simple filtration devices that fit inside curbside drains—remove used motor oil from stormwater run-off. They tested the performance of four commercially available drain inserts, whose various baffles, baskets, screens, fabric bags and filter materials represent the range of technologies on the market.

The research took place in a specially designed on-campus test facility where a row of four washing-machine-sized PVC bins served as mock storm drains. To simulate run-off found in urban areas, the team mixed precise amounts of oil and dirt with water and repeatedly poured the blend through the various drain inserts.

They tested more than 850,000 gallons of synthetic run-off. Unlike real stormwater run-off from Sacramento State, which flows directly into the American River, the synthetic stuff was sent to the local wastewater treatment plant.

None of the four devices was a strong all-around performer. For example, design features that effectively captured oil didn’t capture much sediment. “Devices small enough to fit into a storm drain simply don’t work as well as filters with larger surface areas,” Johnston says. “These results will be useful to cities planning their own stormwater systems.”

The team’s research continues as part of a three-year, multimillion-dollar contract with Caltrans to test stormwater treatment technologies along highways and other Caltrans facilities and to develop a conceptual design for a new kind of drain insert that combines the best features of the four filter devices tested.

“By Christmas it’ll be clear whether we have something we can build and test,” says Johnston. If it looks promising, Caltrans will sponsor fabrication and testing at the campus test facility with the hope the new device could be adopted statewide.